This invention relates to measurements of clearances, and more specifically, to an apparatus and method for measuring or selectively adjusting a clearance between two objects such as a stationary object and a rotating object.
Rotating systems typically have clearances or gaps to avoid contact or rubs during operation due to manufacturing tolerances and thermal expansion or mechanical strain effects. Undesirably, clearances generally result in loss of efficiency of the system. For example, in a pressurized system, clearances cause loss in efficiency due to blowby or degradation of pressure ratios. Typically, manufacturing and design costs increase as attempts are made to reduce the size of clearances in a system.
In a jet turbine engine, for example, a clearance exists between the thin-walled casing and the tips of the rotor blades. The thin walled casing is designed so that during operation it can be heated or cooled to vary the size of the clearance between the casing and the tip of the blade particularly during start-up and shutdown. Rotating systems having a thick casing, however, can not be readily resized by heating or cooling the thick casing to adjust the clearance between the casing and a rotor blade tip.
Therefore, there is a need for a low cost, on-line apparatus and method for measuring a clearance between objects and selectively adjusting and optimizing the clearance during operation.